Establishing and sustaining N2 fixing symbioses between diatoms and cyanobacteria

N2 fixing planktonic partnerships are important symbiosis to study because they are widespread, contribute significantly to both new and primary production, and are little studied.

The symbiotic partners are specific for their hosts and differ dramartically in genome size and content which is linked to their cellular location.

The symbionts function in providing N, and we hypothesize that the hosts support their symbionts for specific precursors, e.g., proline, polyamines, that cannot be synthesized by the symbionts but are necessary for their function.

Second, we hypothesize that provision of high concentrations of reduced N from the symbionts is necessary for establishing these partnerships.

Experiments are designed with stable isotopes and both natural symbiotic diatoms and artificial associations of model diatoms and N2 fixing cyanobacteria, including mutants for increased disasolveed N release from the symbionts.

In some experiments the cellular vesicles that localize around the symbiont filaments will be collected and analyzed as a potential mechanism for N transfer.

Despite their global significance, how the symbioses persist and the symbiont transmittance between generations is unstudied, and as such we will attempt to identify what factors are required for cell division synchronicity and partner propagation.

Given their biogeochemical role, it is important to study how these symbioses replicate and to study their metabolic interactions on a cellular level.